Field of the Invention
The disclosure relates to a foldable display device and more particularly to a backplate for a foldable display device for preventing damage during folding-unfolding operation and a foldable display device including the backplate.
Discussion of the Related Art
As information technology and mobile communication technology have been developed, a display device for displaying a visual image has also been developed. Flat panel display devices, such as a liquid crystal display (LCD) device and an organic light emitting display (OLED) device, are developed and used.
In general, an LCD device includes a liquid crystal panel, which in turn, includes upper and lower substrates and a liquid crystal layer therebetween. The liquid crystal layer is driven by an electric field induced between a pixel electrode and a common electrode to display images.
The OLED device includes an emitting diode, which includes an anode, a cathode and an organic emitting layer therebetween, and holes and electrodes respectively from the anode and the cathode are combined and emits the light in the organic emitting layer to display images.
Recently, the needs for a foldable display device, which is fabricated by using a flexible substrate, are increased. The foldable display device is folded to be portable and is unfolded to display images. Namely, with the foldable display device, the large size image display can be provided, and portability of the display device is improved.
FIG. 1 is a schematic cross-sectional view of the related art foldable display device. As shown in FIG. 1, the foldable display device 10 includes a display panel 20, a backplate 30 and a cover window 40. The display panel 20 includes a flexible substrate 22, a display part 24 on the flexible substrate 22. For example, the flexible substrate 22 may be a polyimide substrate.
When the display panel 20 is an emitting diode panel, the display part 24 may include an emitting diode and a thin film transistor (TFT) for driving the emitting diode. The emitting diode may include an anode, which is connected to the TFT, an organic emitting layer on the anode, and a cathode on the organic emitting layer. In addition, an encapsulation film for preventing moisture penetration may cover the emitting diode.
On the other hand, when the display panel 20 is a liquid crystal panel, the display part 24 may include a thin film transistor (TFT) on the flexible substrate 22, a pixel electrode connected to the TFT, a counter substrate facing the flexible substrate 22, a common electrode on the flexible substrate 22 or the counter substrate, and a liquid crystal layer between the flexible substrate 22 and the counter substrate. The display panel 20 may further include a backlight unit.
With a carrier substrate (not shown) attached to a lower surface of the flexible substrate 22, elements such as the TFT are formed on the flexible substrate 22, and the carrier substrate is released to obtain the flexible display panel 20.
In the flexible display panel 20, since the flexible substrate 22 is too thin, the backplate 30 for supporting the display panel 20 is disposed under the flexible substrate 22. For example, the backplate 30 may be formed of polyethylene terephthalate (PET) and may be attached to the display panel 20 by an adhesive layer 32.
The cover window 40 is attached to an upper side of the display panel 20. The damage on the display panel 20 from outer impacts is prevented by the cover window 40. Although not shown, the cover window 40 may be attached to the display panel 20 by an adhesive layer.
In the related art foldable display device, the PET film having about 100 micrometers is used for the backplate 30. When the folding and unfolding operation is repeated in the foldable display device 10, the plastic deformation occurs in the backplate 30 such that the restoration of the folded display device to its original confirmation becomes difficult.
Namely, as shown in FIGS. 2A and 2B, since there is the plastic deformation problem in the backplate 30 (of FIG. 1) of the PET film, there are limitations in the folding and unfolding operation of the foldable display device 10. Namely, the folding and unfolding characteristic of the foldable display device 10 is deteriorated. FIG. 2A illustrates the backplate 30 plastic deformed such that the backplate 30 does not revert to its original shape when external force is removed. In FIG. 2B shows the result of plastic deformation of the backplate 30 after a repeated folding and unfolding where a center portion 54 is plastic deformed downward and two wing portions 52 are plastic deformed upward.
By reducing a thickness of the backplate 30, the plastic deformation problem in the backplate 30 may be decreased. However, the elastic restoring energy of the backplate 30 having the reduced thickness is decreased such that the time for the restoration of the folded display device is increased.